1. Field of the Invention
This invention relates to a wire bonding device, and in particular to a wire bonding device wherein a position to be bonded can be specified while viewing its image on a monitor.
2. Description of the Background
In the manufacture of semiconductor devices, the wire bonding step, wherein a bonding pad on a semiconductor pellet and an inner lead are electrically connected by bonding wires, is a very important step. A special wire bonding device is used for this step. To carry out wire bonding, the bonding position coordinates have to be input to this wire bonding device. The most usual method of inputting these coordinates is to perform a teaching operation in which the object on which wire bonding is to be performed is locally magnified by a TV camera and displayed as an image on a monitor. The operator carries out an operation of specifying the coordinates at which bonding is to be performed, while viewing this image on the monitor. The sequence of operations is as follows:
(1) The XY stage of the bonding device is moved and adjusted so that a point on the object, which is to be the starting point of the first wire, is displayed at a central position of the monitor image. After this adjustment has been completed, a prescribed input switch is operated to store the coordinates of this starting point in RAM in the bonding device. This is called the teaching operation.
(2) Next, the same teaching operation is carried out for the coordinates of the point that is to be the end point of the first wire, and these are stored in RAM.
(3) The above steps (1) and (2) are carried out sequentially for all the wires.
(4) Lastly, revision and alteration are carried out by again performing steps (1) and (2) for the wires whose position is required to be revised and altered. If revision is to be carried out by a bodily parallel shift of all the bonding positions, the amount of parallel shift for both axes can be set by an operation similar to the teaching operation shown in step (1).
In the teaching operation above described, the operator specifies the bonding positions while viewing the image on the monitor. Reference marks are used as an aid for carrying out this alignment. An example of the reference marks which are displayed on the monitor is shown in FIG. 1 and consists of a reference mark 1 arranged in the form of a cross, and rectangular reference mark 2. The operator aligns a target pattern on the object with the central position on the monitor using these reference marks as a guide.
However, the accuracy of alignment of conventional devices is adversely affected by the fact that it is difficult to always display the most appropriate reference marks for the various different target patterns. For example, when connecting the bonding pads on a semiconductor pellet and the ends of inner leads by wire bonding, the bonding positions must be specified while alternately displaying the bonding pad and the end of the inner lead on the monitor. However, since the bonding pad and inner leads are of different shape and size, precise alignment cannot be achieved using the same reference marks.
To overcome this problem, a device has been designed wherein a rectangular pattern 2 can be set having the desired size and height/width ratio. However, this device is complicated and troublesome to operate because the size of the rectangular pattern and height/width ratio must be changed for each different target pattern from the bonding pad to the inner leads.